In many wireless communication scenarios, the characteristics of the wireless channel fluctuates due to the changes in the propagation environment or the relative movement of transmitter and receiver. As a result, the quality of the wireless link established over that channel between two nodes can be compromised. For example, a satellite in communication with a mobile base station can suffer from reduced signal quality due to atmospheric conditions, such as storms and other similar phenomena. By example, FIG. 1 is a diagram of a city environment with many buildings 10 of different sizes and shapes proximate to a car carrying or having integrated within, a wireless base station 14. The base station 14 is in wireless communication with a satellite 16 to receive an inbound signal 18. For example, a satellite 16 in communication with the mobile base station 14 can suffer from reduced signal quality due to the movement of the base station 14 which can deviate the orientation of base station antenna away from the satellite 16. Other phenomena such as an atmospheric condition 20 or reflection of the inbound 18 and outbound 22 signals from the surrounding buildings 10 can also have similar effects.
In general, the satellite 16 and the base station 14 may have relative movement to each other. By example, such wireless enabled mobile systems can include laptop computers and other portable computing devices such as smart phones and wearable devices. In the present age of the Internet of things (IoT), ground vehicles, airplanes and ships are now being outfitted with computing devices with wireless communication capabilities to enable complex mission-critical functions such as autonomous piloting and to provide relatively simple services such as entertainment media and Internet connectivity. In such examples, these wireless enabled mobile systems can communicate with a satellite and/or a wireless base station. Even when the base station 14 is not mobile, the satellite may not be geosynchronous, therefore in such a case the ground station should steer its receive and transmit beams to track the moving satellite.
While the example of FIG. 1 illustrates an outdoor application where two wireless nodes can establish a link there between, indoor applications are possible as well, where devices with respective wireless transceivers need to establish a link in order to communicate information with each other. In indoor applications, both nodes can be stationary, or one can move relative to the other. Accordingly, similar challenges are faced by indoor wireless systems as the outdoor wireless system shown in FIG. 1.
Ideally, the base station 14 and satellite 16 have a direct and unimpeded line of sight signal propagation path between each other in which an antenna of the base station 14 is configured to receive and transmit signals to the satellite 16 with optimum signal characteristics. An optimum signal characteristic can include signal to noise ratio (SNR), signal power, signal to interference ratio (SIR) etc.
Unfortunately in reality, the wireless transmission environment is similar to that shown in FIG. 1 where the direction of final received inbound signal 18 that reaches the base station 14 can constantly change due to the physical environment. Optimally the receiving beam of the antenna should point to the direction from which the wave is coming, i.e. direction 18, and the transmitting beam of the antenna should point to direction 22 that is parallel to that of inbound signal 18. The antenna of the base station 14 can be physically directed towards the direction 18/22, or in the case where the antenna is implemented as an active phased array antenna, beamforming techniques can be used to achieve the same effect. Those skilled in the art will understand that beam forming is a technique in which each sensor of an array of sensors can be independently configured to provide constructive interference of received or transmitted copies of the same wireless signal. Alternatively self-phased antennas can be used which are able to direct their transmit signal in the opposite direction from which they receive a signal.
An adaptive antenna can respond to the changes in the wireless channel and (partially) compensate the link degradation by optimizing its radiation pattern. Adaptive array antennas are the fusion of flexible pattern antennas and intelligent algorithms controlling the radiation pattern. The antenna part is usually an active phased array antenna (APAA) capable of electronic beam forming. APAA's are well-known in the art.
As is known in the art, in reception (Rx), the received signal strength or some other characteristics of the received signal can be used as a feedback to find and apply the optimal beam forming coefficients to the APAA in order to obtain the optimum signal characteristic for maximizing any desired quality of service (QoS) aspect. For example, a high signal to noise ratio (SNR) of the signal may be required in some applications. However, in transmission (Tx) there is no feedback to send a signal for reception with an optimized characteristic by the satellite 16, or other source node. In one possible solution for the example of FIG. 1, the base station 14 can include an active phased array antenna or a self-phased antenna in order to utilize the information of Rx beam to steer the Tx beam toward the same direction.
Conventional phased array antennas known in the art require characterization and/or calibration of the antenna array in order to accurately estimate the direction of source node and determine the optimal beam forming coefficients for transmitting a signal toward that source node. By example, the physical layout and orientation of each antenna module in the array of antennas must be known relative to each other and to the environment they are installed within. The characteristics of the electronics used in each antenna module comprising the array antenna must be known as they may also perform differently under different temperature conditions. Using the characterization data, the phased array can be calibrated for its non-idealities.
In the example of FIG. 1, a calibrated active phased array antenna at base station 14 can estimate the direction of incoming signal 18 and transmit in the opposite direction 22. Another type of active phased arrays known as fully passive phased arrays which require passive (and preferably low loss) phase shifters that have true delay line behavior over the range of transmit and receive frequency. The later type of phased arrays may not require characterization/calibration. However, the requirements of such phase shifters have limited their feasibility for many applications.
There are many conventional designs based on self-phasing techniques which can be used, but suffer from at least one of the following shortcomings: a) The antenna must be constantly illuminated by a single tone wave know as pilot (or beacon) tone; b) The antenna cannot operate at different Tx and Rx frequencies; c) The antenna cannot handle phase modulated signals or it needs to be redesigned for different modulation schemes; and d) The antenna is unable to steer its beam toward a specific signal source when there are more than one.
A significant amount of wireless communications are between devices in which at least one is mobile and/or the environment between the two ends of communication changes. Therefore there is a need to provide a method and system for determining optimum beam forming coefficients for an antenna array that optimizes at least one characteristic of an inbound received and outbound transmitted signal to a source node, that is low cost, does not require complex calibration procedures and computation, and does not suffer from at least one of the shortcomings outlined above in the conventional solutions.